Pressure centrifuge



v, 2,928,592 Patented Mar. 15, 1960 ice PRESSURE CENTRIFUGE Oscar W. Johnson, Houston, Tex., assignor to Dorr- Oliver Incorporated, Stamford, Conn., a corporation of Delaware Application May 1, 1957, Serial No. 656,425 4 Claims. (Cl. 233-46) This invention relates generally to centrifuges of the type having a rotor suspended from a top mounted shaft and adapted to carry out, at elevated pressures, the continuous separation and discharge of separated overflow and underflow fractions from a feed material containing suspended particles. More particularly, the invention relates to improved ways and means enabling compensation for axial upward thrust exerted by pressure within such a centrifuge thereby to maintain stable operation even when such pressure exceeds the weight of the rotor.

In general, the invention relates to centrifuges of the type disclosed in Patents Nos. 1,923,454, 1,847,751 and 2,060,236 which comprise generally a rotor housing, a rotor suspended in such housing and mounted for rotation therein on a central shaft, said shaft being in turn journalled for rotation in bearings adjacent only its upper end. More specifically, the invention is directed to centrifuges as above discussed but adapted for operation under elevated pressures as disclosed in the co-pend ng application of Kenneth D. Lewis et al., Serial No. 624,524, filed November 27, 1956, which discloses a pressured centrifuge comprising generally a rotor housing, a rotor suspended in such housing, a flexibly mounted bearing spaced above such rotor housing in which the rotor shaft is mounted for rotation, and flexible sealing means interconnecting the bearings and housing. The bearing housing is flexibly mounted to allow slight undulous motion of the rotor and rotor shaft under conditions of rotor unbalance caused by momentary variations in feed distribution. The flexible sealing means, in combination with a shaft seal, provides means for maintaining pressure within the rotor housing.

In the above type of construction, the pressure maintained within the rotor housing creates a force which tends to destroy, in part, the rotational stability of the rotor and shaft assembly. This force acts in an upwardly direction at the bearing assembly and is proportional to the cross sectional area of the upper inner face ofthe flexible closure housing, the cross sectional area of the shaft and the operating pressure maintained within the rotor housing. The effect of this force is to tend to displace the rotor, rotor shaft and the bearing housing in an upwardly direction. 1

As previously mentioned, the bearinghousing is flexibly mounted to allow for slight undulations of the rotor caused by temporary unbalance. Thus, this force, act ing through the shaft and shaft seal housing, tends to cause the flexibly mounted bearing housing to be upwardly displaced and away from its resilient mountings. If the force so exerted is equal to or greater than the weight of the rotor and rotor shaft, the bearing housing willbe displaced from the resilient mountings and the rotor will become free floating. Even if this force is not'o'f great enough magnitude to equal the weight of the rotor and rotor shaft, thestabilit'y of the rotor still will be partially destroyed to a proportionate extent.

The flexible mounting of the bearing assembly incorporates a spring bias which acts to maintain the bear 2 ing housing seated on the resilient mountings. Whileit is theoretically possible to bias the housing with sutli ciently heavy springs to exert a downward force to balance the upward force caused by the pressure within the rotor assembly, such method is not functionally sound in practice due to the enormity of the spring bias required. Further, such method would not have flexibility under conditions of varying operating pressures.

It is, therefore, an object of this invention to provide: ways and means to offset, at least in part, the upward. lifting force of confined pressures in the rotor housing.

A further object is to provide ways and means whereby the material undergoing treatment is employed to off-- set, at least in part, the above described upward forces...

A still further object is the provision of ways and; means whereby energy imparted to the material during; separation is utilized to create a downward force on the: rotor and thus partially offset the undesirable effects of' the upward force component.

A related object is the provision of apparatus and a: method for operating same by which a mass of material. undergoing treatment is maintained in the bottom of the rotor housing and is used to offset, at least in part, the upward force component of the pressure within the rotor housing while simultaneously providing a liquid bottom bearing to give axial support to the rotor and dampen oscillatory movement.

Other and more specific objects will become apparent from the following description read in connection with the accompanying drawing which forms a part of this specification, it being understood, however, that such description is illustrative only and is not to be taken as limiting the invention, the scope of which is defined by the appended claims rather than by the description preceding them.

In the drawing:

The single figure is a cross-sectional view, partially in elevation, illustrating a centrifuge incorporating the pres ent invention.

The centrifuge illustrated in the drawing comprises generally a rotor 11 carried by a vertical shaft 12 and disposed within a stationary rotor housing 13. The machine is provided with a feed inlet 20, a feed passage 14, an overflow passage 16 for discharging a centrifugally separated lighter fraction, an underfiow passage 17 for discharging a centrifugally separated underflow fraction; and a passage 18 for-introducing a supplemental fluid m'aterial which may be heavier centrifugally separated discharge material or underflow. The rotor shaft 12 is connected by a coupling 19 'to a vertical'shaft 21 which is journalled for rotation in a bearing assembly 22 which is in turn housed-in a flexibly mounted bearing housing 23, as more fully described hereinafter.

As is conventional, the rotor housing 13 can be conveniently formed of separable sections 13a, 13b, and 13c of which section 13a forms a volute chamber 24 for 7 receiving separatedoverflow, and section 13b is formed to provide an annular chamber 26v for receiving cen-- trifugally separated heavier or underflow material. p

The body of rotor 11 can likewise be formed from a number of separable parts, including, in the embodiment. illustrated, a main part 11a and upper and lower conical shaped parts llb and respectively. The main part 11a has an inner structure 27'which isattached to'the:

lower end of rotor shaft 12. Parts 11a and 11b-are re- 5 V conduit 54 which is valved as at 53.

r v 3 t Wall 33 ofmain rotor portion 11, each of such nozzles being provided with a discharge orifice directed upwardly with respect to the chamber 2:6 and'preferably backwardly with respect to the rotation of rotor 11. The underflow fraction discharged into an'nular chamber 26'is collectedin co nical bottom chamber 38 adjacent the lower end oftherotor 11 1 "Continuous centrifuges, such asdisclosed in Patents 1,923,454, 1,847,751; and 2,060,236, may be provided with means to return a portion of the separated'under flow to the centrifugerotor. Accordingly,the separated underflow fraction is collected in bottom chamber 38 of rotor housing 13c and may be partially returned to the r'otoiflviaorificeflfi through the action ofscrew type impellet 39,. A conduit47,valved as at 46, provides means fofwijthdrawing controlled quantities of the underflow.

t act n fromchainber 38; A1 valved conduit 52 promeans'ffortihtroducing wash liquid into chamber 38 491.,Spray, nozzles arepositioned around the y of rotor housing 13b which serve to break 'rnfwithi n chamb er 38. For simplicity, only one.

4 o mechanical seal manufactured by Durarnetallic Corporation of Kalamazoo, Michigan.

Bearing oil may be supplied to the bearing assembly 22 in a conventional manner and drained out through conduit 81. Sealing fluid, under pressure, may be supplied to shaft seal 66 via a conduit 82 and discharged via a c0nduit83.

In operation,- pressureswithin-rotor housing 13 will tend to lift bearing housing 23 from its resilient mountings 64, and act against the force of the sprinlgs 63. This force is proportional to the cross'sectional area of the lower inner face 69 of bearing housing 23, the cross sectional area of shaft 21 and the pressure Within the rotor housing. it can be seen that if this forceis great enough, it may balance or even exceed thetweight of the rotor,

the shaft, and the spring bias. If the upward force bea comes so sufficient, the rotor will be lifted off of theres'p ra'y nozzle 56 is herein shown, receiving liquid; via

Toprevent an undesirable swirling plurality of baflles or vanes 57; Such vanes are f fl iuted in, si itahle manner on thewall of rotor hous ing portionlfaetand extend substantially the entire height thereof. Such vanes, operate in the ,mannendisclosedin l lnited statespatent2,625,321, and, as noted above, prevent swirling; oftthe, collected underfiow fraction.

As prexiously noted, a portion of the underflow fracti n and-Wash liquid in chamber 38 are pumped through orifice. 18,, by;t he.actionof screw impeller 39 and into N movementofthe r collected underflow fraction within (bottom chamber, 38, a there i P Q i Q- L hQ-19W?! pa tr rotor ous g 3c,

silient mountings and muchgof thelateral stability of the rotor, willbe; destroyed. Stated diflerently,:whenthe rotor. is mountedonlyjadjacentitsupper end and this upper mounting hastno apparent weight ,due to a balance of upward pressure forces1and the downward weight and.

spring forces, the, rotor becomes free'fioating with but little'stability i'n-regardttozupsetting'lateralforces. Furthat,theglateralistability of the'rotor-will bepartially dexstroyed toyaaproportionately lesser extent; 7

son, it is necessary to. compen'sateforthese upward come the-lower. part of rotor 110 where the material is acted upon by radially extending verticalwebs or vanes 41 which serve to impart rotational velocity to thematerial. Such material passes throughspaces between webs 41g andthen outwardly, through returnitubes or, passages 42,to, pass through main separating chamber 29 which communicates with discharge nozzles 32. V

.Overfiow passage16 islprovided with 'a plurality' of disehargemozzles. 15.1 adjacent the upper end of upper] rotor. sectionllb, Eachof thesenozzlesls are provided-v with a dischargev orifice directed upwardly with respect tovolutexhamber fl and :splash plate 25.

Bearing housing 23zis=fiexibly mountedon shafts- 62g and.iresilientfmountings 64% and is held in position i by 'springsi634 Thisfiexible mounting allows-for eccentric movements of shaft 12-caused by slight inequalities of feedildistributiontin rotor 11. Asthis'centrifuge is-desig'nedato operate under conditions of elevated pressures, itis necessary to sealushaft 21 between the bearinghousing 23 and -rotor housing 13; In the embodiment of this invention as illustrated in the figure, this is accomplished 1 a V by rneans of a telescopic rubber hose 67.] Thus, the elevated pressures'within chamber 68, caused by the, fact thatit fis in free conimunicationwith the rotor housing 1 13?,via passage, 58, are contained therein by .fler rihle hose 67' and ""shaft seal.66..' Other means .for preventing the esgapeof elevated pressure: maybe used, suchas described in th a.

pending 5 application of Kenneth D} Lewis -et 5al., G57 fSh f gseal 66 ;is mounted on shaft -21and in bearing, ho s ng 23-.in,s uch a manner that it moves; withthelshaft ous ing; during moments ,of eccentric movestantiallyhigher than atmospheric pressures of feedmather; even though thepupward forces are not so sufli'cient to equalor exceedthe downward forces, it is apparent ponentsz of; forceoccasion'ed by the'operatin'g pressures inthis type of pressurecentrifuge.

The present invention partially overcomes'the upward pressure force. componentsthrohgh properdisposition andutilization of hoth the overflowand' the underflow fractions; As previously "mentioned, overflow nozzles 15 and1underflow'nozzles=32: are positioned totdischarge up waidly againstthe-T'lower: surfacetof splash: plate 25 and theupper; inner: surface gofiannular receiving chamber 26 6 respectively" Thus, the' kinetic-energy of the overflow andunderflow. fractions-areutilized' to create "forces acting in a downwardly'direction and opposed" toithe lift forces occasioned by the? pressures withinrthe' rotor housing;

A third compensating'forceiis established theiaction t of imp'eller 39i, Asthis; impeller functions'to. pump liquid: from lower chamber;38; into lower rotorsection 110, a downward'forcecomponentiwith respect toi the rotor will, be developed: and: tendvto: offset the-rupward forces of the pressure withirrthehrotorqhousingtg Also, since impeller y 39; is partially, submerged in i the :liquid at theibottomgof chamber,- it will tend'ztotacttasi a bottom liquid :beariingand-thuszhave a stabilizingueifectlon rotor 11. 1

1. Apparatus for the centrifugal separation; at subterialinto a lighteroverllow; fraction and a heavier underflow fractiom-comprising a1 rotor, a: rotor housing,- a rotonshaft; and a rotorshaft bearing; assembly; said rotor housing comprising a vessel surrounding;,sa1d-rotor and pted? Q:' 1 1a .-.sub.stantial y sher t an tm p er pressures said r or housingghaving anioverflow receivi'ng-seetiong; an -;1.inderflow re ceivingsection, and an opening,to aeeonimodate, saidirotorlshaft; said rotor being supported aby said ;rotor,shaft and, comprising feed material inlet 1 means, underflow discharge -means, and overflow discharge ;1 meansg-eaid rot or shaft being journaled for rotation at one -of ;it s endsjn said bearing assembly, a d qt kshaft m a atti xedlyiettasliedin sea iq e a ns pt e i For this reat ertieally from; said bearing P sh-said en 241 aid w hQu n a d.

a], theiotherone-of itsends;:,

, adaptedrto, contain substantiallv er haat t io her c. pre sur t q d a a t rqtor spas-pea ends to said housing and fixedly attached in sealing rela-t tionship at its other end to said bearing assembly; said bearing assembly being spaced from said rotor housing and yieldably mounted to enable axial movements of said rotor shaft in relationship to said rotor housing; the improvement which comprises jet means associated with said underfiow discharge means peripherally mounted on said rotor and positioned to discharge said underfiow fraction in a direction that will create an axial thrust on said rotor shaft away from the bearing assembly of said rotor shaft.

2. Apparatus according to claim 1 in which jet means are associated with said overflow discharge means mounted on said rotor and positioned to discharge said overflow fraction in a direction that will create an axial thrust on said rotor shaft away from the bearing assembly of said rotor shaft.

3. Apparatus according to claim 1 in which said bearirlilg assembly is at the upper axial extent of said rotor s aft.

4. Apparatus according to claim 3 in which a liquid impeller is fixedly mounted adjacent the lower end of said rotor, said liquid impeller extending into said underflow receiving section of said rotor housing and being adapted to impel a portion of the underflow fraction from the bottomsection of said rotor housing into said rotor.

1,923,454 Peltzer et al. Aug. 22, '1933 Coe Mal-f1, 1932 

